Database and Application Security

1
Database and Application Security

• S. Sudarshan
• Computer Science and Engg. Dept
• I.I.T. Bombay

2
Database Security

• Database Security - protection from malicious
  attempts to steal (view) or modify data.

3
Importance of Data

• Bank/Demat accounts
• Credit card, Salary, Income tax data
• University admissions, marks/grades
• Land records, licenses
• Data crown jewels for organizations
• Recent headlines
• Personal information of millions of credit card
  users stolen
• Laws on privacy in the US
• Theft of US data in India
• Criminal gangs get into identity theft
• Earlier this year in Mumbai
• Hackers steal credit card data using card reader
  and make fraudulent purchases
• Hacker creates fake Web site to phish for credit
  card information
• Auto-rickshaw license fraud in New Delhi

4
Identity Theft

• Pretend to be someone else and get credit
  cards/loans in their name
• Identification based on private information
  that is not hard to obtain online
• More lucrative than blue-collar crime,
• harder to catch criminals
• Hurts victims even more than regular theft
• Onus goes on innocent people to prove they didnt
  get loans or make credit card payment
• Credit history gets spoilt, making it harder to
  get future loans
• And you may have been robbed without ever knowing
  about it.
• Increasing risk in India
• PAN numbers, names available online

5
What me worry?

• Bad things only happen to other people.??
• SQL/Slammer
• Attacked SQLServer, brought networks down all
  over the world (including IITB)
• Luckily no data lost/stolen
• Flaw in registration script at database security
  workshop at IIT Bombay
• Careless coding exposed database password to
  outside world
• Most Web applications vulnerable to SQL injection
  attacks

6
Overview

• Levels of data security
• Authorization in databases
• Application Vulnerabilities
• Summary and References

7
Levels of Data Security

• Human level Corrupt/careless User
• Network/User Interface
• Database application program
• Database system
• Operating System
• Physical level

8
Physical/OS Security

• Physical level
• Traditional lock-and-key security
• Protection from floods, fire, etc.
• E.g. WTC (9/11), fires in IITM, WWW conf website,
  etc.
• Protection from administrator error
• E.g. delete critical files
• Solution
• Remote backup for disaster recovery
• Plus archival backup (e.g. DVDs/tapes)
• Operating system level
• Protection from virus/worm attacks critical

9
Database Encryption

• E.g. What if a laptop/disk/USB key with critical
  data is lost?
• Partial solution encrypt the database at storage
  level, transparent to application
• Whole database/file/relation
• Unit of encryption page
• Column encryption
• Main issue key management
• E.g. user provides decryption key (password) when
  database is started up
• Supported by many database systems
• Standard practice now to encrypt credit card
  information, and other sensitive information

10
Security (Cont.)

• Network level must use encryption to prevent
• Eavesdropping unauthorized reading of messages
• Masquerading
• pretending to be an authorized user or
  legitimate site, or
• sending messages supposedly from authorized
  users

11
Network Security

• All information must be encrypted to prevent
  eavesdropping
• Public/private key encryption widely used
• Handled by secure http - https//
• Must prevent person-in-the-middle attacks
• E.g. someone impersonates seller or bank/credit
  card company and fools buyer into revealing
  information
• Encrypting messages alone doesnt solve this
  problem
• More on this in next slide

12
Site Authentication

• Digital certificates are used in https to prevent
  impersonation/man-in-the middle attack
• Certification agency creates digital certificate
  by encrypting, e.g., sites public key using its
  own private key
• Verifies site identity by external means first!
• Site sends certificate to buyer
• Customer uses public key of certification agency
  to decrypt certificate and find sites public key
• Man-in-the-middle cannot send fake public key
• Sites public key used for setting up secure
  communication

13
Security at the Database/Application Program

• Authentication and authorization mechanisms to
  allow specific users access only to required data
• Authentication who are you? Prove it!
• Authorization what you are allowed to do

14
Database vs. Application

• Application authenticates/authorizes users
• Application itself authenticates itself to
  database
• Database password

Application Program
Database
15
User Authentication

• Password
• Most users abuse passwords. For e.g.
• Easy to guess password
• Share passwords with others
• Smartcards
• Need smartcard
• a PIN or password

16
User Authentication

• Central authentication systems allow users to be
  authenticated centrally
• LDAP or MS Active Directory often used for
  central authentication and user management in
  organizations
• Single sign-on authenticate once, and access
  multiple applications without fresh
  authentication
• Microsoft passport, PubCookie etc
• Avoids plethora of passwords
• Password only given to central site, not to
  applications

17
Overview

• Levels of security
• Authorization in databases
• Application Vulnerabilities
• References

18
Authorization

• Different authorizations for different users
• Accounts clerk vs.
• Accounts manager vs.
• End users

19
Database/Application Security

• Ensure that only authenticated users can access
  the system
• And can access (read/update) only data/interfaces
  that they are authorized to access

20
Limitations of SQL Authorization

• SQL does not support authorization at a tuple
  level
• E.g. we cannot restrict students to see only (the
  tuples storing) their own grades
• Web applications are dominant users of databases
• Application end users don't have database user
  ids, they are all mapped to the same database
  user id
• Database access control provides only a very
  coarse application-level access control

21
Access Control in Application Layer

• Applications authenticate end users and decide
  what interfaces to give to whom
• Screen level authorization which users are
  allowed to access which screens
• Parameter checking users only authorized to
  execute forms with certain parameter values
• E.g. CSE faculty can see only CSE grades

22
Access Control in Application Layer

• Authorization in application layer vs. database
  layer
• Benefits
• fine grained authorizations, such as to
  individual tuples, can be implemented by the
  application.
• authorizations based on business logic easier to
  code at application level
• Drawback
• Authorization must be done in application code,
  and may be dispersed all over an application
• Hard to check or modify authorizations
• Checking for absence of authorization loopholes
  becomes very difficult since it requires reading
  large amounts of application code
• Need a good via-media

23
Oracle Virtual Private Database

• Oracle VPD
• Provides ability to automatically add predicates
  to where clause of SQL queries, to enforce
  fine-grained access control
• E.g. select from grades becomes
  select from grades where rollnouserId()
• Mechanism
• DBA creates an authorization function. When
  invoked with a relation name and mode of access,
  function returns a string containing
  authorization predicate
• Strings for each relation and-ed together and
  added to users query
• Application domain hosted applications, where
  applications of different organizations share a
  database (down to relation level)
• Added predicates ensures each organization sees
  only its own data

24
Privacy

• Aggregate information about private information
  can be very valuable
• E.g. identification of epidemics, mining for
  patterns (e.g. disease causes) etc.
• Privacy preserving data release
• E.g. in US, many organizations released
  anonymized medical data, with names removed,
  but zipcode ( pincode), sex and date of birth
  retained
• Turns out above (zipcode,sex,date of birth)
  uniquely identify most people!
• Correlate anonymized data with (say) electoral
  data with same information
• Recent problems at America Online
• Released search history, apparently anonymized,
  but users could be easily identified in several
  cases
• Several top officials were fired
• Earlier problems revealed medical history of
  Massachusetts state governer.
• Not yet a criminal issue, but lawsuits have
  happened
• Conflict with Right To Information Act
• Many issues still to be resolved

25
Overview

• Levels of security
• Authorization in databases
• Application Vulnerabilities
• References

26
Application Security

• Applications are often the biggest source of
  insecurity
• Poor coding of application may allow unauthorized
  access
• Application code may be very big, easy to make
  mistakes and leave security holes
• Very large surface area
• Used in fewer places
• Some security by obfuscation
• Lots of holes due to poor/hasty programming

27
OWASP Top 10 Web Security Vulnerabilities

• Unvalidated input
• Broken access control
• Broken account/session management
• Cross-site scripting (XSS) flaws
• Buffer overflows
• (SQL) Injection flaws
• Improper error handling
• Insecure storage
• Denial-of-service
• Insecure configuration management

28
SQL Injection

• E.g. application takes accnt_number as input from
  user and creates an SQL query as follows
• string query "select balance from account where
  account_number " accnt_number ""
• Suppose instead of a valid account number, user
  types in
• delete from r
• then (oops!) the query becomes
• select balance from account where account_number
  delete from r
• Hackers can probe for SQL injection vulnerability
  by typing, e.g. in an input box
• Tools can probe for vulnerability
• Error messages can reveal information to hacker

29
Preventing SQL Injection

• To prevent SQL injection attacks use prepared
  statements (instead of creating query strings
  from input parameters)
• PreparedStatement pstmt conn.prepareStatement(
  "select balance from account where
  account_number ?)pstmt.setString(1,accnt_numbe
  r)pstmt.execute()
• (assume that conn is an already open connection
  to the database)
• Alternatives
• use stored procedures
• use a function that removes special characters
  (such as quotes) from strings

30
Passwords in Scripts

• E.g. file1.jsp (or java or other source file)
  located in publicly accessible area of web server
• Intruder looks for http//lturlpathgt/file1.jsp
• or .jsp.swp, etc
• If jsp has database userid/password in clear
  text, big trouble
• Happened at IITB
• Morals
• Never store scripts (java/jsp) in an area
  accessible to http
• Never store passwords in scripts, keep them in
  config files
• Never store config files in any web-accessible
  areas
• Restrict database access to only trusted clients
• At port level, or using database provided
  functionality

31
Outsider vs. Insider Attack

• Most security schemes address outsider attack
• Have password to database? Can update anything
• Bypassing all application level security measures
• More people with access ? more danger
• Application program has database password
• Great deal of trust in people who manage
  databases
• Risk of compromise greater with value of data
• Happened with auto-rickshaw registration in New
  Delhi

32
Protecting from Users

• Multi-person approval
• Standard practice in banks, accounts departments
• Encoded as part of application workflow
• External paper trail
• Strong authentication of users
• Smart cards
• Careful allocation of authorizations on a need to
  use basis
• Practical problem absence of a user should not
  prevent organization from functioning
• Many organizations therefore grant overly
  generous authorizations

33
Protecting from Programmers/DBA

• Have password to database, can update anything!
• Digital signatures by end users can help in some
  situations
• E.g. low update rate data such as land records,
  birth/death data
• Application program has database password
• Seize control of the application program ? can do
  anything to the database
• Solution
• Dont give database password to development team
• keep password in a configuration file on live
  server, accessible to only a few system
  administrators
• Ongoing research on trusted applications
• E.g. OS computes checksum on application to
  verify corruption
• Allows file-system access only to trusted
  applications

34
Protection from admin/super-users

• Operating system administrators (also known as
  super-users) can do anything they want to the
  database.
• Small number of trusted administrators
• What if a laptop with critical data is lost?
• Encrypt entire database (and/or file system)
• Supported, e.g. in SQL Server 2005
• Authentication (password/smart card) when
  database is started up

35
Detecting Corruption

• Audit trails record of all (update) activity on
  the database who did what, when
• Application level audit trail
• Helps detect fraudulent activities by users
• Independent audit section to check all updates
• BUT DBAs can bypass this level
• E.g. audit trail apparently deleted in New Delhi
  auto-rickshaw license case by malicious users
  with DBA access
• Database level audit trail
• Database needs to ensure these cant be turned
  off, and turned on again after doing damage
• Supported by most commercial database systems
• But required DBAs with knowledge of application
  to monitor at this level
• Keep archival copies and cross check periodically

36
Information Leakage

• So you thought only the query result matters?

37
Information Leakage via UDFs

• Auth view myemployee only those employee whose
  dept_id is in A1
• Query
• select from employee where myudf(salary)
• Final query plan is not safe
• UDF may be pushed down in plan, and executed on
  unauthorized intermediate result
• As a side-effect, UDF may expose values passed to
  it Litchfield
• Can be partly solved using sandboxing

38
Other channels of information leakage

• Exceptions, Error Messages
• Query select from employee
  where 1/(salary-100K) 0.23
• Query plan Selection condition in query gets
  pushed below authorization semi-join
• Divide by zero exception if salary 100K
• Reveals that employee has salary 100K
• Timing Analysis
• Sub-query can perform an expensive computation
  only if certain tuples are present in its input
• To prevent leakage, treat all channels as unsafe
  operations

39
Preventing Information Leakage via UDFs

• UDF on Top Keep UDFs at the top of query plan
• Definitely safe, no information leakage
• Better plans possible if UDF is selective
• Optimal Safe plan
• When is a plan safe?
• How to search for optimal safe plan?
• For details, see Kabra et al., SIGMOD 2006

40
Overview

• Levels of security
• Authorization in databases
• Application Vulnerabilities
• Summary

41
Summary

• Data security is critical
• Requires security at different levels
• Several technical solutions
• But human training is essential

42
Acknowledgments

• Pictures in this talk stolen from various web
  sources!

43
References

• (Shameless advertisement!) Chapter 8 of Database
  System Concepts 5th Edition, Silberschatz, Korth
  and Sudarshan, McGraw-Hill
• The Open Web Application Security Project
• http//www.owasp.org
• Web application security scanners
• e.g. WebInspect (SPI Dynamics)
• http//www.windowsecurity.com/software/Web-Applica
  tion-Security/
• SQL Injection
• http//www.cgisecurity.com/development/sql.shtml
• 9 ways to hack a web app
• http//developers.sun.com/learning/javaoneonline/2
  005/webtier/TS-5935.pdf
• Related research papers
• Kabra, Ramamurthy and Sudarshan, Redundancy and
  Information Leakage in Fine-Grained Access
  Control, SIGMOD 2006
• Rizvi, Mendelzon, Sudarshan and Roy, Extending
  Query Rewriting Techniques for Fine-Grained
  Access Control, SIGMOD 2004

44
Extra Slides
45
Authorization

• Forms of authorization on (parts of) the
  database
• Read authorization - allows reading, butnot
  modification of data.
• Insert authorization - allows insertion of new
  data, but not modification of existing data.
• Update authorization - allows modification, but
  not deletion of data.
• Delete authorization - allows deletion of data

46
Security Specification in SQL

• The grant statement is used to confer
  authorization
• grant ltprivilege listgt
• on ltrelation name or view namegt to ltuser listgt
• ltuser listgt is
• a user-id
• public, which allows all valid users the
  privilege granted
• A role (more on this later)
• Granting a privilege on a view does not imply
  granting any privileges on the underlying
  relations.
• The grantor of the privilege must already hold
  the privilege on the specified item (or be the
  database administrator).

47
Privileges in SQL

• select allows read access to relation,or the
  ability to query using the view
• Example grant users U1, U2, and U3 select
  authorization on the branch relation
• grant select on branch to U1, U2, U3
• insert the ability to insert tuples
• update the ability to update using the SQL
  update statement
• delete the ability to delete tuples.
• references ability to declare foreign keys when
  creating relations.
• usage In SQL-92 authorizes a user to use a
  specified domain
• all privileges used as a short form for all the
  allowable privileges

48
Privilege To Grant Privileges

• with grant option allows a user who is granted a
  privilege to pass the privilege on to other
  users.
• Example
• grant select on branch to U1 with grant option
• gives U1 the select privileges on branch and
  allows U1 to grant this
• privilege to others

49
Roles

• Roles permit common privileges for a class of
  users can be specified just once by creating a
  corresponding role
• Privileges can be granted to or revoked from
  roles
• Roles can be assigned to users, and even to other
  roles
• SQL1999 supports roles
• create role tellercreate role manager
• grant select on branch to tellergrant
  update (balance) on account to tellergrant all
  privileges on account to managergrant teller to
  managergrant teller to alice, bobgrant
  manager to avi

50
Revoking Authorization in SQL

• The revoke statement is used to revoke
  authorization.
• revokeltprivilege listgt
• on ltrelation name or view namegt from ltuser listgt
  restrictcascade
• Example
• revoke select on branch from U1, U2, U3 cascade
• Revocation of a privilege from a user may cause
  other users also to lose that privilege referred
  to as cascading of the revoke.
• We can prevent cascading by specifying restrict
• revoke select on branch from U1, U2, U3 restrict
• With restrict, the revoke command fails if
  cascading revokes are required.

51
Revoking Authorization in SQL (Cont.)

• ltprivilege-listgt may be all to revoke all
  privileges the revokee may hold.
• If ltrevokee-listgt includes public all users lose
  the privilege except those granted it explicitly.
• If the same privilege was granted twice to the
  same user by different grantees, the user may
  retain the privilege after the revocation.
• All privileges that depend on the privilege being
  revoked are also revoked.

52
Secure Payment

• Three-way communication between seller, buyer and
  credit-card company to make payment
• Credit card company credits amount to seller
• Credit card company consolidates all payments
  from a buyer and collects them together
• E.g. via buyers bank through physical/electronic
  check payment
• Several secure payment protocols
• E.g. Secure Electronic Transaction (SET)